In recent years, it has become possible to obtain a polyketone comprising a substantially alternating copolymer of carbon monoxide and an olefin such as ethylene or propylene by polymerizing carbon monoxide with said olefin by using a transition metal complex of palladium, nickel or the like as a catalyst (Kogyo-zairyo, the December number, page 5, 1997). A large number of investigators have investigated the application of polyketones as fiber for industrial materials, and it is expected that the polyketones will be utilized as fiber for composite materials, such as reinforcing fiber for tire cords, belts and the like, and reinforcing fiber for concrete, by taking advantage of the high strength, high modulus of elasticity, high-temperature dimensional stability, adhesive properties and creep resistance of the polyketones.
Since the polyketones are easily crosslinked by heat when melted, wet spinning is preferably employed for producing fiber from the polyketone. In particular, polyketones obtained substantially from only carbon monoxide and ethylene (poly(1-oxotrimethylene)s; hereinafter abbreviated as ECO) which can exhibit excellent mechanical properties is easily crosslinked by heat and hence is very difficult to melt-spun, so that fiber thereof can be obtained substantially only by wet spinning.
As a solvent used in the wet spinning of the polyketone, there are known hexafluoroisopropanol, phenolic solvents such as m-cresol, resorcinol/water, etc., and organic solvents such as resorcinol/carbonate, etc. All of these solvents, however, involve serious problems when used for conducting the wet spinning industrially.
For example, JP-A-2-112413 and Japanese Patent Application Kohyo No. 4-505344 disclose wet spinning processes of aliphatic polyketones and the employment of any of hexafluoroisopropanol, m-cresol and a mixture thereof as a solvent. In particular, Japanese Patent Application Kohyo No. 4-505344 discloses that as to characteristics of solvents including the above solvents, solvents having a dipole moment of 3×10−30 to 9×10−30 coulomb meter and a Hildebrand solubility parameter of 16 to 27 MPa−1/2 can be used as a solvent for the polyketones. Hexafluoropropanol, however, cannot be industrially used for the following reasons: it is so expensive that its industrial employment is utterly unprofitable even when a trifling loss of hexafluoropropanol in its recovery is considered; and hexafluoropropanol has a high toxicity and a low boiling point, so that a completely closed spinning equipment should be used. On the other hand, m-cresol can be used as a solvent for the aliphatic polyketones, but it should be used in combination with hexafluoro-isopropanol because of its low dissolving power and it has a high toxicity and a strong odor of phenol, so that a completely closed spinning equipment should be used. Moreover, fiber obtained by using any of the above solvents has unsatisfactory mechanical properties, and the production of fiber from a solution containing any of the above solvents becomes difficult at a rapid spinning rate in some cases because the rate of desolvation from the solution is too slow.
JP-A-4-228613, Japanese Patent Application Kohyo No. 7-508317 and Japanese Patent Application Kohyo No. 8-507328 disclose the employment of a solvent comprising at least one aromatic alcohol, and mention resorcinol/water, phenol/acetone, hydroquinone/propylene carbonate, and resorcinol/propylene carbonate as specific examples of the solvent. These aromatic alcohols, however, have a high toxicity and a strong odor of phenol, so that a completely closed spinning equipment should be used. Furthermore, when a combustible organic solvent is used in combination with them as a co-solvent, an explosion-proof equipment is necessary. In addition, since the solubility of ECO in the mentioned solvents is not always sufficient, the polymer concentration in the resulting dope cannot be increased, so that the attainment of a high strength is difficult. In the case of resorcinol/water, the desolvation rate is too slow when coagulation using water is carried out, and hence methanol should be used as a coagulation bath, so that expensive and complicated spinning equipment and solvent-recovering equipment should be used.
A problem to be solved by the present invention is to provide a polyketone solution not obtained by the use of the well-known solvent for polyketone described above, i.e., a polyketone solution which has a low toxicity, is excellent in incombustibility, spinning stability and solvent recoverability, is inexpensive, and can be industrially subjected to wet spinning; a process for producing polyketone fiber by subjecting said polyketone solution to wet spinning; and polyketone fiber.